Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

611
FXUS63 KLOT 120500
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1100 PM CST Thu Dec 11 2025

.KEY MESSAGES...

- A clipper system may produce a few inches of powdery snow
  accumulation in areas mainly south of Interstate 80 on
  Saturday.

- Very cold temperatures and bitterly cold wind chills are
  expected this weekend with wind chills below zero.

- There is a growing signal for a pattern change toward milder
  (and less snowy) conditions next week.

&&

.UPDATE...
Issued at 851 PM CST Thu Dec 11 2025

Recent radar imagery augmented by surface observations and
webcams depict the northern edge of snow associated with the
much advertised clipper system extends from La salle toward
Cissna Park, IL. North of this line, a wedge of dry low-level
air has relegated all radar returns (including a separate band
from northeastern Iowa into southwestern Wisconsin) to virga
(snow not reaching the ground). Expansive cloud cover is once
again holding temperatures in the low to mid 20s.

Snow is expected to continue south of a line from La Salle to
Cissna Park through the next 2 to 4 hours, perhaps accumulating
up to an inch or two. Will have to watch for snow associated
with the aforementioned secondary band currently across
northeastern Iowa and southwestern Wisconsin to reach the ground
in northern IL over the coming hours, though suspect the wedge
of dry low-level air will continue to chew up all the snowflakes
before the reach the ground. So, will go ahead and tighten up
the gradient in PoPs and snow accumulations to focus on our far
south and maintain dry conditions elsewhere through the night.

After midnight, both observational and model trends suggest
that at least partial clearing will take place from northwest to
southeast. As a result, do suspect temperatures have a better
shot of falling tonight compared to last night, especially with
northwestward extent. The inherited forecast already has this
idea handled well, so no other changes to the gridded database
were needed.

Updated products are out.

Borchardt

&&

.DISCUSSION...
Issued at 156 PM CST Thu Dec 11 2025

Through Friday:

The primary forecast focus continues to center on the next
quick moving clipper system expected to produce a 100 to 150
mile wide swath of accumulating snow across portions of the
region tonight. Forecast guidance, in conjunction with recent
regional radar and satellite observations, continue to focus
this swath of snow well southwest of the Chicago metro area,
roughly from southeastern IA southeastward through central IL
and southern IN. Across this region, a rather robust mesoscale
frontogenetic response is expected to develop for a few hour
period late this afternoon into this evening along the
tightening lower level baroclinic zone. This is likely to result
in an even narrower band of moderate to briefly heavy snow
rates (0.5 to 1" per hour) for a couple hours early this
evening. This will particularly be the case across central
portions of IL just to the southwest of my area where a Winter
Weather Advisory is in effect.

Snow rates outside of the main band will be much lighter
(generally a 0.5" or less per hour), particularly with
northeastward extent across LaSalle, Livingston, Ford and
Iroquois counties. In these areas, 1 to as much as 3" are
possible (highest in the southern portions of the counties).
Snow amounts will then tapper quickly with northeastward extent,
with little or no snow accumulation anticipated across most of
northeastern IL and far northwestern IN. Of the accumulations
that occur in my southwest counties, much of them will occur
this evening, with rates quickly tapering off overnight. Some
occasional flurries and/or light snow showers may persist across
portions of the area very into early Friday morning,
particularly near the IL Lake Michigan shore. However, lake
effect parameters are not expected to be overly impressive, so
little in the way of additional accumulation is anticipated.

Conditions on Friday will continue to be largely mostly cloudy.
Temperatures will also remain chilly, with highs generally in
the 20s to low 30s. Some occasional light snow or flurries may
also occur at times, particularly across northern IL during the
day as another weak impulse passes over WI. Little if any
accumulation is expected with this activity.

KJB


Friday Night through Thursday:

Cold front will move across the CWA Friday evening with much
colder air spilling south into the area in the wake of the
front. There could be a few flurries lingering into Friday
evening, but not looking for any organized or measurable
precipitation. Confidence in just how cold temperatures will get
Friday night is a bit on the lower end of the spectrum. NBM and
global guidance are quite cold with lows ranging from near 0
northwest CWA to around 10 southeast CWA. The heart of the
arctic air mass doesn`t look to arrive until later Sat or Sat
evening, so it`s plausible that those low temps are a bit too
cold. Didn`t make any changes to the NBM at this point since
even if the ambient temp is 4-5F warmer it is still going to
feel very cold and really won`t change the message.

An Alberta Clipper is progged to dive southeast into the Midwest
and phase with the tropospheric polar vortex over the Great
Lakes Saturday. Medium range guidance the past couple of days
has generally been on a gradual shift southward with the axis of
accumulating snow with this feature. Despite the trends in
GFS/GEFS and ECMWF/EPS, medium range guidance often struggles
with phasing and its quite plausible that there could still be
some sizable latitudinal changes in where the axis of
accumulating snow lays out Saturday. Current guidance would
favor our southern CWA south into central IL which is where NBM
has the highest pops and accums. Given the potential for this to
shift north or further south still, felt chance pops offered up
by the NBM up to the WI border looked reasonable.

Secondary push of arctic air is expected in the wake of that
clipper with the coldest air mass expected over the area
Saturday night into Sunday morning. Surface high looks to remain
well west of the region Saturday night, so despite clearing
skies, anticipate we`ll maintain some wind (10-15 mph). This
wind combined with what looks to be widespread subzero air temps
should push wind chills into the 15 to 25 below zero range
across the area.

Winds will gradually ease during the day Sunday and skies should
be clear, but only offering up deceptive sunshine as
temperatures should remain very cold. Many areas could struggle
to get out of the single digits above zero for highs. Even with
easing winds, wind chills during the day Sunday will probably
remain near or below zero.

Sunday night`s low temps are tricky and will likely depend
significantly on the exact location of the sfc high. If the high
is overhead or nearby, then a rapid evening temp drop to well
below zero could occur, however if the high is already moving
off to the east by evening, then developing southerly winds
could temper the evening temp fall. Guidance currently suggests
that the high will move well east of the area by early Monday
morning, so southerly winds should pick up overnight and result
in rising temps. The rise in temps will likely be partially
offset by the strengthening winds resulting in wind chills
remaining bitterly cold.

Medium range guidance continues to suggest a pattern change to a
more zonal flow across the country next week. This would tend to
keep the colder air bottled up to our north Canada with a return
to normal and probably eventually above normal temperatures.

- Izzi

&&

.AVIATION /06Z TAFS THROUGH 12Z SATURDAY/...
Issued at 1100 PM CST Thu Dec 11 2025

Forecast concerns for the terminals...

- MVFR ceilings to return Friday afternoon.

- Increasing west-northwest winds Friday evening with 20-25 kt
  gusts expected.


A clipper system continues to pivot through IL this evening
which has lead to a band of snow across south-central IL and IN.
While the accumulating snow will remain well south and west of
the terminals, there is a chance for a period of light snow
showers and flurries to occur tonight along and south of a La
Salle, IL to Fowler, IN line.

Otherwise, expect light and variable winds to persist through
tonight before winds settle into a westerly direction Friday
afternoon. Wind speeds will gradually increase into Friday
evening as a cold front moves through the area with 20-25 kt
gusts expected behind the front. As for ceilings, the 2500-3000
ft MVFR ceilings earlier this evening have continued to erode
beneath an area of 10000 ft clouds with most sites now reporting
VFR conditions. While a period of MVFR clouds may still ooze in
off of Lake Michigan at the Chicago area terminals, it appears
VFR conditions should prevail through tonight. However, MVFR
ceilings will return ahead of the aforementioned cold front
Friday afternoon and should linger through the conclusion of the
TAF period.

Yack

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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